Interposer assemblies with molded plastic plates and metal contacts inserted in the plates are used for forming electrical connections between contact pads on opposed substrates. The contacts and pads are spaced very close together in land grid array rows and columns to establish a large number of differential pair signal and ground connections extending through the plate.
Conventional interposer assemblies use contacts formed from metal strips with contact ends which engage pads on the substrates. Each contact is fitted in a passage extending through the plate. The strip has two functions. It establishes a circuit path between pads on opposed substrates and it includes a spring which provides contact pressure at the pads. Sandwiching an interposer assembly between opposed substrates compresses the contacts in the assembly plate to stress the springs and provide contact pressure required for good electrical connections between the contacts and pads.
Conventional interposer assembly contacts have inefficient springs with limited energy storage in the strip due to a single mode of elastic beam strain concentrated in the ends of the contact at the top and bottom of the plate. Spring performance can be increased by forming the contacts from copper strip stock with expensive performance-enhancing alloys, such as beryllium copper. Use of these alloys undesirably increases the cost of the contacts.
Thus, there is a need for an interposer assembly for forming reliable electrical connections between opposed substrate pads using contacts, preferably formed from metal without expensive strengthening alloys, where the contacts are both highly conductive and highly compliant to assure reliable electrical connections between pads.
The springs in the contacts should be mechanically efficient so that compressed energy is stored through elastic strain in the contacts and is recovered when the substrates are removed from engagement with the contacts. Frictional loss, due to engagement between the contacts and the walls of the contact passages extending through the plate, should be minimized. Compliance of the contact and reliable electrical connections with the opposed pads should be enhanced.